Yossie, Rika, Kei, Ogawa, and Konno were all listed as "solo artists" right after their graduations, and Tsuji and Mari later - so - I wouldn't hold my breath.
To comment on the Aika "hate" - it isn't hate. Just because people don't think she has added ANYTHING to Morning Musume in the past 5 years other than a few flat notes doesn't mean it's "hate" - it's an opinion.
I feel REALLY bad for her, I'm sure she's a sweet girl and I don't think she should have left so soon, but will she be missed from the future Morning Musume? No, not really. She was never a big part of the group and the past year she hasn't been part at all, so the transition is going to be even more smooth than I think it naturally would've been anyway.
Yeah there are some bitches still bitter that she "took Kikkawa's spot" - but seriously, those people are very few and far between. I just don't think she's been an asset at all, and I don't think she'll be missed. People are just being wishy-washy right now bc she is graduating, as it always goes.